Shelf Sea Biogeochemistry blog

Saturday, 22 August 2015

Collecting images from the seafloor.

By Henry Ruhl

We have completed sediment core sampling at our four main study sites. This is a key achievement for the trip. We are now sampling one other site that allows us to cross-reference our findings with those of other studies and a long-term study station with the nickname Candyfloss. This site is closer to the continental shelf edge and open ocean than we have been for most of the trip. Marine life spotting has been good and we even laid eyes on the RRS James Cook about ten miles from us. The James Cook is researching life in the canyons that extend just beyond the shelf edge. We will soon return northward to for the more AUV deployments, the fourth deployment of the NOC lander, as well as a few other remaining tasks.

We are using the Autsub3 autonomous underwater vehicle (AUV) during our cruise to collect photographic images of the seafloor, as well as sonar-based images of the shape and texture of the seafloor. We have been running the AUV in a ‘mowing the lawn’ pattern of parallel lines that are about ~5km long. After checking our seafloor shape and texture mapping for any obstacles, we ‘fly’ the AUV as close as 2.5 meters from the seafloor to collect colour photographs in the moderately cloudy waters of the Celtic Sea.

The images will be geo-referenced, which effectively turns the photo into a map like you see in Google Earth. As you can see below, that 2.5 m height above the seafloor still gives us images that are very useful for determining the identity size, and location of all the observed images. This can provide a landscape scale view of the seafloor and its inhabitants, which we can then use to improve estimates of ecological and biogeochemical patterns and processes.

The seafloor and its inhabitants
AUV photographs are particularly useful in estimating the distribution of biomass of larger animals that are not sampled well by trawls or sediment cores. Observed animals include crabs, shrimps, and anemones as well as fish. The images above and below come from a Celtic Sea site where the seafloor is dominated by sandy mud.

The seafloor and its inhabitants

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